Imaging plasticity and structure of cortical maps in cat and mouse visual cortex
b'The study reported in the first part of this thesis utilized optical imaging of intrinsic signals to\\nvisualize changes in orientation maps in cat visual cortex induced by pairing a visual stimulus\\nwith an intracortical electrical stimulation. We found that the direction of plasticity within\\norientation maps depends critically on the relative timing between visual and electrical\\nstimulation on a millisecond time scale: a shift in orientation preference towards the paired\\norientation was observed if the cortex was first visually and then electrically stimulated. In\\ncontrast, the cortical response to the paired orientation was diminished if the electrical preceded\\nthe visual cortical stimulation. Spike-time-dependent plasticity has been observed in single cell\\nstudies; however, our results demonstrate an analogous effect at the systems level in the live\\nanimal. Thus, timing-dependent plasticity needs to be incorporated into our conception of cortical\\nmap development.\\nWhile the pairing paradigm induced pronounced shifts in orientation preference, the general setup\\nof the orientation preference map remained unaltered. In order to unravel potential factors\\ncontributing to this overall stability, we determined the distribution of plasticity across the cortical\\nsurface. We found that pinwheel centers, points were domains of all orientation meet, exhibited\\nless plasticity than other regions of the orientation map. The resistance of pinwheel centers to\\nchanges in orientation preference may support maintenance of the general structure of the\\norientation map.\\nThe study that forms the second part employs optical imaging to visualize the retinotopy in mouse\\nvisual cortex. We were able to resolve the pattern of retinotopic activity with high precision and\\nreliability in the primary visual cortex (area 17). Functional imaging of the position, size and\\nshape of area 17 corresponded exactly to the location of this area in stained histological sections.\\nThe imaged maps were also confirmed with electrophysiological recordings. The retinotopic\\nstructure of area 17 showed very low inter-animal variability, thus allowing averaging maps\\nacross animals and therefore statistical analysis. These averaged maps greatly facilitated the\\nidentification of at least four extrastriate visual areas. In addition, we detected decreases in the\\nintrinsic signal below baseline with a shape and location reminiscent of lateral inhibition. This\\ndecrease of the intrinsic signal was shown to be correlated with a decrease in neuronal firing rate\\nbelow baseline.\\nBoth studies were facilitated by the development of a signal analysis technique (part III), which\\nimproves the quality of optical imaging data. Intrinsic signal fluctuations originating from blood\\nvessels were minimized based on their correlation with the actual superficial blood vessel pattern.\\nThese fluctuation components were then extracted from images obtained during sensory stimulation. This method increases the reproducibility of functional maps from cat, rat, and mouse\\nvisual cortex significantly and might also be applied to high resolution imaging using voltage\\nsensitve dyes or functional magnetic resonance.'